modem answering at wrong speed

[Marty Connor]

In article <273 at mjbtn.UUCP> root at mjbtn.UUCP (Mark J. Bailey) writes:
>I am having an annoying problem that some of you may have also experienced.
>my modems set to answer at 2400 baud and then cycle to 1200 on a CR and then
>back to 2400.  They are supposed to reset to 2400 baud at logoff, aren't 
>they?  Well, what is happening is that on initial setup, they answer the 
>first calls just fine, and then when the user logs off, they answer the 
>next call properly at 2400 baud ... sometimes.  At other times, they seems
>to get "stuck" in a 1200 baud mode, and that is where they stay, regardless

I had the same problem with my Practical Peripherals 2400 baud modems.
Apparently, one *minor* ambiguity with HAYES compatibility is, whether
the modem should ALWAYS answer the phone at the HIGHEST baud rate that
it can do, and then step down.  If a modem answers the phone and
starts making 1200 baud noises, the modem on the other end will not
even bother trying a higher baud rate.  Therein lies the screw.

Well, I convinced the people at Practical Peripherals that I was not
crazy, and that it was broken behavior for a modem to answer at a
1200 baud if it could do 2400, if the modem had been set up with the
AT&C1&D3 command.  They said their gold-standard HAYES did it. I
suggested they get a new HAYES and try it;  I also suggested that even
if HAYES did it, it was broken, and emulating this bug was evil.

Apparently OLDER genuine HAYES modems would answer the phone at the
last baud rate that modem was USED at.  The folks at Practical Peripherals
tell me that newer HAYESes have changed their minds on this.  Nice
folks, these.  They just sent me new ROMs for my PM2400SAs to fix the
bug.  Thanks, Therese, Dave, and Roland (on bass).

Small point, but try autobauding on your Xenix box with the modems
conspiring to play baud-rate roulette.

Anyway, the executive summary is:

   AT&C1&D3
   AT&W

AT&C1 says that the modem should not lie to the host about carrier
detect, but should indicate the true state of the carrier on pin 8.

AT&D3 (this is the biggy) says that the modem should do an ATZ every
time that DTR goes low-then-high.

Hope this make someone's day/night.
-- 
----------------
Marty Connor
Director of Innovation, The Entity
mdc at mcp.entity.com, ...{harvard|uunet}!mit-eddie!spt!mcp!mdc